Gauging head and apparatus for the linear dimension checking of mechanical pieces and associated machining process

ABSTRACT

Gauging head and apparatus for the linear dimension checking of mechanical pieces comprising an integral element ( 1 ) that defined an arm ( 5 ) carrying a feeler ( 25 ), a reference portion ( 3 ), and a fulcrum ( 13 ) that enables rotations of arm ( 5 ) with respect to the reference portion ( 3 ), and a differential transformer position transducer with a cylindrical shaped casing ( 35; 82 ), carrying the windings ( 34; 83 ), fixed to the reference portion ( 3 ), and a ferromagnetic core ( 32; 84 ) movable together with the arm ( 5 ). The integral element ( 1 ) is locked in an adjustable way to a support ( 67 ), by means of the cylindrical casing ( 35; 82 ). The integral fulcrum is achieved by work hardening the material and subsequently grinding it.

TECHNICAL FIELD

The present invention relates to a gauging head suitable for coupling toa support for the linear dimension checking of a mechanical piece,comprising a shaped element defining a first reference portion, a secondportion, or arm, movable with respect to the first, and an intermediateportion, or fulcrum, between the first and the second portion, thatdefines a geometric axis of reciprocal rotation between said first andsecond portion, a feeler fixed to said arm for contacting the piece tobe checked, and a transducer device for providing signals responsive tothe position of the feeler with respect to the reference portion,including two reciprocally movable parts, a first part thereof beingstationary with respect to said first portion of the shaped element, anda second part being movable, together with said arm, with respect to thefirst portion.

The invention also relates to a checking apparatus for the lineardimension checking of a mechanical piece, comprising a support, agauging head with a shaped element defining a first reference portion,stationary with respect to the support, a second portion, or arm,movable with respect to the first, and an intermediate portion, orfulcrum, between the first and the second portion, that defines an axisof reciprocal rotation between said first and second portion, a feelerfixed to said arm for contacting the piece to be checked, and atransducer device for providing signals responsive to the position ofthe feeler with respect to the reference portion, including tworeciprocally movable parts, a first part thereof being stationary withrespect to the first portion of the shaped element, and a second partbeing movable, together with said arm, with respect to the firstportion, and a processing unit, electrically connected to the transducerdevice.

Furthermore, the invention relates to a process for machining the armsetof a gauging, or measuring, head including an integral element thatdefines two reciprocally movable portions and a fulcrum between saidportions.

BACKGROUND ART

There are known gauging heads for the geometric inspection of mechanicalpieces that comprise a measuring arm with a feeler for contacting apiece to be checked, an element for supporting the arm, a fulcrum forallowing displacements of the arm with respect to the support elementand a transducer for providing a signal responsive to the position ofthe arm with respect to the support element, in which the measuring arm,the support element and the fulcrum are formed from a single piece.

An example is provided in U.S. Pat. No. 4,409,737, that disclosesgauging heads in which the support element comprises a wing, thatextends in a direction perpendicular to the arm and enables thecoupling—by means of screws—of the head to an external support. Thistype of coupling is quite lacking in versatility, in that, as thenominal dimensions of the piece to be checked vary, generally there isthe need to replace the feeler and/or couple—by means of screws—the headin another area of the support or to another external support. In orderto guarantee the correct operation of the head, the coupling existingbetween the wing and the external support must be extremely accurate.This involves precision mechanical machinings of the surfaces intendedto be arranged into mutual contact for defining the position of thehead, and particular care in coupling the head to the external support.

Moreover, in the measuring heads disclosed in the US patent, thearrangement of the fulcrum, feeler and transducer is such that thefeeler displacements occurring further to contact with the surface ofthe piece to be checked and the displacements among the reciprocallymovable parts of the transducer substantially occur along two parallelstraight lines, but at a certain distance from each other. Consequently,the entity of the displacement of the elements of the transducer differsfrom that of the corresponding displacement of the feeler and, in orderto process the correct detecting, it is necessary to keep into accountthe so-called “arms-ratio”, i.e. the ratio existing between the distanceseparating the transducer and the feeler from the axis of rotationdefined by the fulcrum. It is understood how undesired displacements inthe position of the axis of rotation of the arm (due to a not entirelyaccurate implementing of the integral fulcrum) and/or flexions of thearm may negatively affect the operation of the head, modify the ratiobetween the feeler and the transducer displacements with respect to thetheoretical condition that considers an “arm ratio” evaluated on thebasis of the head geometry.

The type of material utilized in the heads with armsets and so-called“integral” fulcra normally undergoes a hardening process for the purposeof increasing its ultimate tensile stress and thus its resilient range.This process, apart from being expensive, is subject to other drawbacks.In fact, when the material is ground for thinning it at the point whereit is desired to achieve the fulcrum, especially if it is desired toattain a very thin fulcrum, there is the risk that the material mayconsiderably heat up at the thinned point, and thus loose the effectsthat the hardening process had provided. The materials utilized forhardening must contain carbon and, owing to the fact that they areconsequently oxidable, need a final treatment, like, for example, zincplating.

It is absolutely necessary to employ particularly yielding, and thusvery thin, fulcra when it is required to check pieces having limitedstiffness that could deflect under a high measuring force, or piecesmade of a soft material, that could get scratched.

Because of the need to accomplish precision mechanical machinings,hardening, grinding and subsequent antioxidant treatment, it is evidentthat these gauges are expensive and it is often difficult to attainparticularly thin and yielding fulcra.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide an extremely accurate,versatile, simple to manufacture and inexpensive gauging head thatovercomes the limitations of the known gauging heads.

It is another object of the invention to provide a gauging head that hasa measuring force low enough to permit its use even for checkingresilient pieces.

These and other objects are achieved by a gauging head comprising ashaped element including a first reference portion, a second arm portionmovable with respect to the first reference portion, and an intermediateportion, or fulcrum, between the reference and arm portion, that definesa geometric axis of reciprocal rotation between said reference and armportion, a feeler fixed to said arm portion for contacting the piece tobe checked, and a transducer device for providing signals responsive tothe position of the feeler with respect to the reference portion,including two reciprocally movable parts, a first part thereof beingstationary with respect to said reference portion of the shaped element,and a second part being movable, together with said arm portion, withrespect to the reference portion, wherein the first part of thetransducer device comprises a casing having an elongate shape, locked tothe reference portion and including a coupling surface, said casingbeing adapted for locking to the support at said coupling surface fordefining the position of the gauging head with respect to the support.

Yet another object of the present invention is to provide a checkingapparatus for checking the linear dimensions of mechanical pieces that,apart from guaranteeing considerable accuracy, is extremely simple andcan rapidly and easily be adapted for checking pieces that havedifferent nominal dimensions.

This and other objects are achieved by an apparatus comprising asupport, a gauging head with a shaped element for defining a firstreference portion, stationary with respect to the support, a second armportion movable with respect to the first reference portion, and anintermediate portion, or fulcrum, between the reference and arm portion,that defines a geometric axis of reciprocal rotation between saidreference and arm portion, a feeler fixed to said arm portion forcontacting the piece to be checked, and a transducer device forproviding signals responsive to the position of the feeler with respectto the reference portion, including two reciprocally movable parts, afirst part thereof being stationary with respect to said referenceportion of the shaped element, and a second part being movable, togetherwith said arm portion, with respect to the reference portion, and aprocessing unit, electrically connected to the transducer device of thegauging head, wherein the first part of the transducer device comprisesa casing with an elongate shape, and the support comprises an openingand a locking/unlocking device for housing said casing and adjusting theposition of the gauging head with respect to the support.

A considerable advantage that a gauging head and a checking apparatusaccording to the invention provide is the utmost flexibility, thatenables to employ as transducer devices, both known gauges of varioustypes (axial-sliding or “cartridge” heads, dial type comparators, orothers), and plain transducers (for example, Linear VariableDisplacement Transducers, i.e. “LVDT” transducers) with windings and aferromagnetic core coupled to the reciprocally movable parts of thearmset, respectively. In this second case, an additional advantage thatthe heads according to the invention (and the apparatuses utilizingthese heads) provide, is the friction free operation of the variousmoving, component parts.

An additional object that the invention provides is the attaining of anarmset employed in gauging (or measuring) heads, that is extremelysimple from a structural point of view, and can be manufactured byequally simple, rapid and economically convenient machinings.

This and other objects and advantages are achieved by a processincluding the steps of arranging a bar of metal material, andimplementing a work hardening and a simultaneous reduction of thethickness of at least one area of the bar by compressing the area bymeans of a tool, thereby achieving a filcrum and defining reciprocallymovable portions.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described in more detail with reference to theenclosed sheets of drawings, given by way of non limiting example,wherein:

FIG. 1 is a partly cut-away longitudinal cross-sectional view of achecking apparatus comprising a gauging head according to the inventionwith some details shown in front view,

FIG. 2 is an enlarged scale sectional view of a detail of the head shownin FIG. 1, viewed along line II—II with some parts omitted for the sakeof simplicity, and

FIG. 3 is a partly cut-away longitudinal cross-sectional view, with somedetails shown in front view, of a gauging head according to anotherembodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The checking apparatus shown in FIGS. 1 and 2 comprises a gauging headwith an armset basically consisting of an integral, substantiallyU-shaped, element 1, formed, for example, from a single bar of stainlesssheet-steel. The element 1 includes a first reference portion 3 that hasa substantially rectangular cross-section and a second portion, or arm5, also with a rectangular cross-section. The arm 5 and the referenceportion 3 are formed by bending the stainless sheet-steel bar.

An intermediate portion 13, located between the arm 5 and the referenceportion 3, has a round-shaped recess 9 and a squared groove 11, formedat two opposite sides of the sheet, at a same area, by compressing ordrawing (for example, on a press) and grinding, respectively. In thisway, the intermediate portion 13 has a transversal thickness that isreduced with respect to that of the other portions of element 1 andforms a fulcrum, in other terms it defines a geometric axis of rotationfor the displacements of arm 5 with respect to the reference portion 3.Portion 13 also has a through hole 14 for increasing the compliance ofthe fulcrum.

The upper end of arm 5 has a bent portion 15.

The upper end of the reference portion 3 has a part 17 bent andwithdrawn into itself.

On the bent portion 15 of arm 5 there are two threaded holes 21 and 23,aligned with respect to each other.

A tang 24 of a feeler 25 for contacting a mechanical piece 26 to bechecked is screwed in hole 21.

A transducer device comprises a linear variable displacement transducer27 with a core 32 made of ferromagnetic material and windings 34 thathouse the core. In hole 23 there is screwed a pin 28 to which there isglued a stem 30 that carries the core 32 of the transducer 27.

On part 17 of reference portion 3 there is a threaded hole 33 and twothrough holes 29 and 31 aligned with respect to each other and thethreaded holes 21 and 23.

The transducer 27 comprises a casing 35 with an elongate shape, forexample a cylindrical shape, that houses the windings 34, and is housedin the opening defined by the two holes 29 and 31. Locking elementsincluding a screw 36, that is screwed into the threaded hole 33, enablethe casing 35 to be locked to the reference portion 3 in an adjustableway along a transversal geometric axis of adjustment defined by thecasing 35 itself.

The windings 34 of the transducer 27 are electrically connected, bymeans of a cable 37, to a power supply, processing and display device,schematically shown and identified by reference number 38 in thefigures.

A tubular sealing gasket 39, made of rubber, has an end coupled to arm 5at the bent portion 15 and the other end coupled to the casing 35, so asto protect the transducer 27 from potential damage caused by foreignmatter.

Arm 5 has a cylindrical seat 41 aligned with a threaded hole 43 locatedin reference portion 3.

Thrust devices between the arm 5 and the reference portion 3 of theshaped element 1 comprise a compression spring 45 with an end housed inthe cylindrical seat 41 and the other end coupled to a bushing 47,internally threaded. A dowel 49 has an end screwed into the threadedhole 43 and the other end screwed into the interior of bushing 47. A nut50 abuts against the surface of arm 5 for axially clamping dowel 49.

By operating bushing 47, it is possible to set the thrust of spring 45between arm 5 and the reference portion 3.

The rotations of arm 5 with respect to the reference portion 3 arelimited, in a clockwise and counterclockwise direction (with referenceto FIG. 1), by a mechanical limiting device comprising a screw 51 with athreaded stem that traverses a through hole 53 in arm 5 with a suitableamount of radial clearance and is screwed into a threaded hole 55 of thereference portion 3. On the stem of screw 51 there are screwed threenuts 57, 59 and 61. Nut 57 is urged against the reference portion 3 forpreventing the accidental unscrewing of screw 51. Nut 59 has a base thatdefines an abutting surface for abutting against an internal surface ofarm 5 for limiting the range of the rotational displacements of arm 5 ina clockwise direction (with reference to FIG. 1) and nut 61 is urgedagainst nut 59 for axially locking nut 59 to the stem of screw 51. Therotational displacements of arm 5 in a clockwise direction (withreference to FIG. 1) are limited by contact occurring between theabutting surfaces of the head of screw 51 and the arm 5 itself.

Moreover, the checking apparatus shown in FIG. 1 includes a support 67locked, by means of screws 71, to a base, schematically shown andidentified by reference number 72. As shown in FIG. 2, in the upper partof the aforementioned support 67 there is an opening 73 for access to asubstantially cylindrical hole 75 and two holes 77 and 79, one of thetwo —77— being threaded, aligned along a direction perpendicular to theaxis of hole 75. The gauging head, more specifically the shaped element1, is locked to support 67 by first inserting cable 37 through opening73, by inserting the casing 35 in hole 75 and then locking the casing 35in the required position, by narrowing opening 73. This is done byinserting a screw 80 into hole 79 and screwing it into threaded hole 77.The holes 75, 77 and 79 and screw 80 taken together form alocking/unlocking device that operates on a coupling surface 40, definedby the cylindric casing 35, for locking, in an adjustable way along thetransversal geometric axis of adjustment, the position of the gauginghead with respect to support 67.

The checking apparatus, for checking the diametral dimensions of a shaft26, for example, operates in the following way.

Under rest conditions, the reciprocal position between arm 5 andreference portion 3 is defined by the arrangement of screw 51, and, morespecifically, the contact—under the thrust of spring 45—between externalsurfaces of arm 5 and the reference surface of the head of the formerlymentioned screw 51.

By slackening nut 57 and operating screw 51, it is possible to set theformerly mentioned reciprocal position between arm 5 and referenceportion 3, whereas by slackening nut 61 and operating nut 59, it ispossible to vary the maximum amplitude of rotation of arm 5 commencingfrom the rest condition.

In a first zero-setting phase of the gauging head, the pre-stroke isdefined, i.e. the distance that the feeler must travel, commencing fromthe rest condition, before it reaches zero position. In order to dothis, the reciprocal position, under rest conditions, between core 32and windings 34 of the transducer 27 is defined by operating the lockingelements, more particularly by slackening screw 36 and adjusting theaxial position of casing 35 until the display unit 38, that receives andprocesses the associated signals issued by transducer 27, indicates therequired pre-stroke value, for example 300 μm. At this point, screw 36is clamped onto the coupling surface 40 of casing 35 for setting theposition of the latter on the integral element 1. The head is thencoupled to support 67, by inserting the casing 35 in hole 75. A masterpiece, with a diameter size equal to the nominal one of the shafts to bechecked, is positioned between reference supports, not shown in thefigures, for example, Vee-shaped supports, stationary with respect tothe base 72, in such a way that feeler 25 contacts the surface of themaster piece in a diametral direction. Then, casing 35 is axially slidinto hole 75 until, further to contact occuring between feeler 25 andthe surface of the master piece and the feeler subsequently displacingof an entity equal to the previously defined pre-stroke, display unit 38displays zero value. Then, the locking/unlocking device is operated,and, specifically, screw 80 is clamped onto the coupling surface 40 inorder to lock casing 35, and thus the entire gauging head, to support 67in the position that has been so determined. Upon completing thelocking, possible limited deviations with respect to the value displayedby unit 38 are compensated by operating adjustment potentiometers ofunit 38, per se known and not shown in the figures. At this point theapparatus is ready for checking and the master piece, that had been usedduring the zero-setting phase, is removed from the reference supportsand replaced by the piece 26 to be checked.

Upon contact occurring between feeler 25 and the surface of piece 26,there occurs a rotational displacement of arm 5 in a clockwise direction(with reference to FIG. 1) starting from the rest condition. Thisdisplacement causes a variation in the position of core 32 with respectto the windings 34 of the transducer 27 and the latter provides anelectric signal responsive to the deviation of the diameter size of thepiece 26 taken into consideration for inspection, with respect to thediameter size of the master piece.

If the nominal dimensions of the piece vary (within a relatively broadrange, that depends on the dimensions of the gauging head), the samechecking apparatus and the same supports for the piece reference canstill be used. This is effected by simply altering the position of thehead with respect to support 67 by operating the locking/unlockingdevice (screw 80) and adjusting the axial arrangement of casing 35, byrepeating zero-setting operations similar to those previously described.

The particularly “light” structure of the arm-set of the head, inaddition to the absence of friction among the reciprocally movableelements of the transducer 27 ensures excellent performance at very lowforces (“measuring forces”) between feeler 25 and the surface of thepiece to be checked. This allows, among other things, to employ thegauging head for checking poorly stiff pieces, in other terms in thosecases in which a too high measuring force could deform the piece in thecourse of the measurement taking, and thus generate unreliable and nonrepeatable results.

A typical example is the flatness checking of a broad and flexiblesurface of the casing of an electronic apparatus in which it isnecessary to utilize a plurality of heads for achieving accuratemeasurements. If each of these heads applies to the piece a substantialforce, there may occur not only the piece deformation during thechecking operations, but also that the deformation be irreversible. Inorder to reduce the layout dimensions of the electronic apparatus, oftenthe amount of space between the casing and the circuit boards, housedtherein, that carry the electronic components, is very small. Therefore,it is necessary to check the flatness of the casing surface, but it isalso important not to deform the formerly mentioned surface in order toprevent the casing, once assembled, from contacting the electroniccomponents on the boards. Gauging heads like the one illustrated inFIGS. 1 and 2 are, thus, particularly suitable for checkings of thistype, especially thanks to the possibility of operating at low measuringforces.

According to a second embodiment of the invention, illustrated in FIG.3, there is a structure a great many coincident with that of FIG. 1,insofar as, among other things, the armset with the shaped element 1,the feeler 25, the mechanical limiting device 51, the compression spring45, the locking elements with the screw 36, and the support 67 with thelocking/unlocking device including screw 80 are concerned.

An axial-sliding linear gauge, for example, a cartridge head 81 of a perse known type comprises a substantially cylindrical-shaped casing 82,that houses the windings 83 and the ferromagnetic core 84 of adifferential transformer transducer device, a stem 85, axially movableand partially housed in casing 82, that carries at one end an additionalfeeler 86 and at the other end the core 84, thrust means including anadditional spring 87 that applies to stem 85 a thrust towards theexterior of casing 82, and guide means 88, housed in casing 82, forguiding the displacements of stem 85. The casing 82 of gauge 81 ishoused in holes 29 and 31 in the reference portion 3 of element 1 andthe axial position of the cartridge head 81 is determined, by the screw36 that operates on a coupling surface 91 of casing 82, as describedwith regard to the casing 35 of the transducer 27 shown in FIG. 1. Areference abutment element 89 made of hardened material, locked to thethreaded hole 23 of arm 5, comprises a flat surface 90 for remaining incontact with the additional feeler 86 of the cartridge head 81, ashereinafter described.

The shaped element 1 is locked to support 67 by inserting cable 37through opening 73, by inserting the casing 82 in hole 75 and thenlocking the cartridge head 81 to support 67 in the required position byoperating screw 80 to restrict the opening 73.

The functioning principle of the checking apparatus substantiallycoincides with what has been herein described with reference to FIGS. 1and 2.

When a zero-setting operation on a master piece is performed, theprestroke of the gauging head is firstly defined by adjusting, underrest conditions, the position taken by casing 82 of the cartridge head81 in the opening defined by holes 29 and 31. More specifically, theadditional feeler 86 (integral with the ferromagnetic core 84) isbrought into contact with the surface 90 of the reference abutmentelement 89, and the position of the casing 82 (integral with thewindings 83) is further adjusted until the required pre-stroke value isdisplayed by unit 38. At this point, screw 36 is clamped onto thecoupling surface 91 of casing 82 for locking the position of the latteron the integral element 1. Then, the gauging head is locked to support67 by inserting casing 82 of the cartridge head 81 in hole 75 andadjusting its axial position until the feeler 25 contacts the surface ofthe piece to be measured and, subsequently to a displacement thatrepresents the pre-stroke, the display unit 38 displays a “zero” valuereading.

The master piece is removed and replaced with a piece 26′ to be checkedand the checking operation takes place in the manner hereinbeforedescribed with reference to the first embodiment of the invention. Inthe course of the checking operations, the additional feeler 86 of gauge81 always remains in contact—urged by the thrust of the additionalspring 87—with the surface 90 of the reference abutment element 89 andconsequently displaces integrally with arm 5, exactly in the same way asto what occurs, in the embodiment shown in FIG. 1, to pin 28 thatcarries, by means of stem 30, the core 32 of transducer 27. In this way,the additional feeler 86 and the stem 85—rigidly coupled to thefeeler—undergo just substantially axial strains, caused by thedisplacements of arm 5. Thus, those transversal strains that occur, forexample, in known applications in which the feelers of cartridge headsdirectly contact pieces to be checked and expose the in ternalcomponents of the gauge to undesired strains, are so avoided.

From the foregoing description, the versatility of the invention isevident. In fact, the same armset with the bent element 1 can beemployed in gauging heads with a friction free transducer 27 (FIG. 1)enabling an extremely accurate measurement taking at very low measuringforces, or else in an axial-sliding linear gauge (FIG. 3) or a gauge ofanother type, as, for example, a dial type gauge, whenever similardevices are available and other requirements are necessary (as, forexample, the need to prevent the armset of the linear gauge fromundergoing any transversal strains), though maintain in both cases thesame locking, positioning and zero-setting simplicity.

In fact, the housing defined by holes 29 and 31 and the associatedlocking elements are dimensioned and arranged so as to allow, aspreviously described, the simple and rapid locking of both thewindings—housed in a suitable casing (35)—of a transducer (27) and“standard” size gauges. On the other hand, it is possible to couple—inan equally and obviously rapid and simple way—to the threaded hole 23 inarm 5, aligned with hole 21 that houses the feeler 25, either the pin 28carrying stem 30 and core 32, or the reference abutment element 89 withthe flat surface 90 for maintaining contact with the feeler of a gauge(for example, feeler 86 of the cartridge head 81).

Moreover, the manner according to which the head is locked to thesupport 67, besides providing flexibility and application simplicityadvantages, as hereinbefore described, does not need extremely accuratemechanical machinings of the surfaces of the integral element 1, that donot affect in any way the positioning.

In addition to versatility, one of the main advantages that theinvention provides is the simplicity and low costs for manufacturing thearmset of the head, specifically insofar as the material utilized, theimplemented structure, and the necessary operations are concerned. Infact, the shaped element 1 is formed by bending to a U shape a bar ofstainless sheet-steel, and achieving the fulcrum by drawing, forexample, by using a press for striking a blow to the sheet-steel bar,and subsequently grinding it. By drawing, there is obtained a workhardening of the material and hence an increase of the elastic range atthe point where it is desired to implement the fulcrum. The partundergoing the drawing is then ground for the purpose of obtaining therecess that enables to further lighten the fulcrum and so providelightness and low measuring force, typical characteristics of the head.

Moreover, as the material utilized does not have to undergo a hardeningprocess beforehand, no subsequent antioxidant treatments of the headarmset are necessary, and the material is substantially insensitive,even in the case of very thin and yielding fulcra, to the negativeeffects that the heating generated by the subsequent grinding operationmight have on the ultimate tensile stress of the material (tempering).

A further advantage that the heads herein described and illustratedprovide is a specific high degree of precision and accuracy, thanks tothe aligning between the straight line according to which the feeler 25substantially displaces and the one along which reciprocal displacementamong the parts of the transducer device (32,34;83,84) takes place.

Indeed, this allows the observance of the Abbe principle—whereby inorder to measure a length and benefit by all the measurement accuracy ofthe gauging instrument, it is necessary to arrange the formerlymentioned length along the detecting, or transduction axis. Furthermore,as it is not necessary to keep into account specific “arm ratios”, theprocessing operations in unit 38 are simplified and the detecting issubstantially insensitive to inaccuracies upon defining the rotationaxis by fulcrum 13 and to flexions of arm 5.

It is possible to modify the herein described head and checkingapparatus according to the present invention, without departing from thescope of the invention. For example, it is possible to manufacture thelimiting and/or thrust devices in a known way, that differs from whathas been described, or arrange them in another way.

In particular applications it is also possible to employ a feeleroff-set with respect to the point where it is coupled to the arm. Theshaped element can be manufactured by employing a material differentfrom the stainless sheet-steel and the hardening process can be attainedby following known processes that differ from the drawing process.

It is possible to employ even capacitive, or inductive type, transducerdevices, manufactured in a different way from the one herein described.

Furthermore, by means of a machining process according to the presentinvention, it is possible to manufacture an armset with an integralelement similar to the one illustrated and described, suitable forapplications differing from those illustrated and that can be employed,for example, in absolute measuring heads.

Moreover, the herein described process for manufacturing the fulcrumalso applies to the machining of armsets that have other shapes, as, forexample, arm-sets with a plurality of fulcra and a so-called“parallelogram” type structure.

What is claimed is:
 1. Gauging head suitable for coupling to a supportfor the linear dimension checking of a mechanical piece comprising ashaped element including a first reference portion, a second arm portionmovable with respect to the first reference portion, and a filcrum,between the reference and arm portions, that defines a geometric axis ofreciprocal rotation between said reference and arm portions, the gauginghead further including a feeler fixed to said arm portion for contactingthe piece to be checked, and a transducer device for providing signalsresponsive to the position of the feeler with respect to the referenceportion, including two reciprocally movable parts, a first part thereofbeing stationary with respect to said reference portion of the shapedelement, and a second part being movable, together with said armportion, with respect to the reference portion, wherein the first partof the transducer device comprises a casing having an elongate shape,locked to the reference portion and including a coupling surface, saidcasing being adapted for locking to the support at said coupling surfacefor defining the position of the gauging head with respect to thesupport.
 2. A gauging head according to claim 1, wherein said elongateshaped casing defines a transversal geometric axis of adjustment, thereference portion of the shaped element comprising an opening andlocking elements for enabling the locking of the first part of thetransducer device to the reference portion of the shaped element, in aposition adjustable along said transversal geometric axis, therebydefining the position of the shaped element with respect to the support.3. A gauging head according to claim 1, wherein said first and secondpart of the transducer device comprise windings, housed in said casing,and a core made of ferromagnetic material, housed within the windings,respectively.
 4. A gauging head according to claim 1, wherein saidcasing of the transducer device has a substantially cylindrical shape.5. A gauging head according to claim 1, wherein said second part of thetransducer device is coupled to the arm of the shaped element.
 6. Agauging head according to claim 5, wherein said transducer devicecomprises a tubular sealing gasket with ends coupled to said arm andsaid casing, respectively.
 7. A gauging head according to claim 4,wherein the transducer device comprises an axial-sliding gauge thatincludes said substantially cylindrical-shaped casing, a stem, axiallymovable with respect to the casing, that carries at one end said coreand at the opposite end an additional feeler, and thrust means forurging said additional feeler to contact a surface integral with the armportion of the shaped element.
 8. A gauging head according to claim 2,wherein said feeler is coupled to the arm portion of the shaped elementin a position that is substantially aligned with said transversalgeometric axis of adjustment.
 9. A gauging head according to claim 1,wherein the shaped element is made of bent sheet metal.
 10. A gauginghead according to claim 9, wherein the shaped element is made ofstainless material.
 11. A gauging head according to claim 10, whereinthe shaped element is made of stainless steel.
 12. A gauging headaccording to claim 11, wherein said fulcrum is achieved by a compressionand a subsequent grinding operation.
 13. A gauging head according toclaim 1, including thrust devices between said arm portion and saidreference portion with a compression spring that cooperates with saidarm portion and said reference portion.
 14. A gauging head according toclaim 1, comprising a mechanical device for limiting the reciprocaldisplacements of said arm portion with respect to said referenceportion, with an element coupled to one of said reference and armportion of the shaped element and comprising abutting surfaces forcooperating with the other of said reference and arm portion.
 15. Agauging head according to claim 9, wherein said geometric axis ofreciprocal rotation is defined by a compression of the sheet metal atthe fulcrum of the shaped element.
 16. Checking apparatus for the lineardimension checking of a mechanical piece, comprising a support, and agauging head with a shaped element for defining a first referenceportion, stationary with respect to the support, a second arm portionmovable with respect to the first reference portion, and a fulcrum,between the reference and arm portions, that defines a geometric axis ofreciprocal rotation between said reference and arm portions, the gauginghead further including a feeler fixed to said arm portion for contactingthe piece to be checked, and a transducer device for providing signalsresponsive to the position of the feeler with respect to the referenceportion, including two reciprocally moveable parts, a first part thereofbeing stationary with respect to said reference portion of the shapedelement, and a second part being movable, together with said armportion, with respect to the reference portion, and a processing unit,electrically connected to the transducer device of the gauging head,wherein the first part of the transducer device comprises a casing withan elongate shape, and the support comprises an opening and alocking/unlocking device for housing said casing and adjusting theposition of the gauging head with respect to the support.
 17. Anapparatus according to claim 16, wherein said elongate shaped casingincludes a coupling surface and a transversal geometric axis ofadjustment, the locking/unlocking device cooperating with said couplingsurface for locking, in an adjustable way along said transversalgeometric axis, the position of the gauging head with respect to thesupport.
 18. An apparatus according to claim 17, wherein said feeler iscoupled to the arm portion of the shaped element in a position that issubstantially aligned with said transversal axis of adjustment.
 19. Anapparatus according to claim 18, wherein said shaped element is made ofbent stainless sheet-steel.